If you go
Subaru Telescope: Located on the Mauna Kea summit, on Hawaii's Big Island, about 31/2 hours from either Hilo or Kona; www.subarutelescope.org or (808) 934-5056. Daytime 30-minute tours are offered free, up to 15 weekdays a month at 10:30 a.m., 11:30 a.m. and 1:30 p.m. Tours are conducted in English, Japanese or both. Reservations are required and should be made early; tour schedules are posted on the Web site two months in advance. Children under 16, pregnant women and those with health conditions that make them susceptible to altitude sickness are not permitted on the tours.
Getting there: A four-wheel drive vehicle is needed to get to the summit of Mauna Kea. Some car rental agencies prohibit driving on Saddle Road (which bisects the island and is the only route to the summit access road), so check beforehand. Also, watch out for cattle or feral pigs wandering into the road.
High altitude: A stop at Onizuka Center for International Astronomy Visitor Information Center -- www.ifa.hawaii.edu/info/vis or (808) 961-2180 -- is highly recommended to help acclimate to the altitude. The visitor center is at 9,000 feet; the summit is nearly 14,000 feet. Allow at least 30 minutes to adjust. Stopping on the way down also is advised.
Tips: The nearest stores, gas stations and medical assistance are at least an hour away from the visitor center, so take provisions with you. Warm clothing, including gloves and hats, and water are essential. Also, there are few restrooms beyond the visitor center.